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Ancient Star Found, Estimated at 13.2 Billion Years Old
raguirre writes "An article on Physorg.org reports that a newly found star may be as old as the universe itself. Recent studies have concluded that the Big Bang occurred somewhere in the neighborhood of 13.7 Billion years ago. The star, a heavy-elements laden fossil labeled HE 1523-0901 on charts was probably born right around the same time; approximately 13.2 Billion years ago. 'Today, astronomer Anna Frebel of the the University of Texas at Austin McDonald Observatory and her colleagues have deduced the star's age based on the amounts of radioactive elements it contains compared to certain other "anchor" elements, specifically europium, osmium and iridium.'"
Because of the higher density of the universe back then, the first few dozen generations of star were probably all super-massive giants that only have a lifespan of between 10 and 100 million years. The first supernova-generated elements were introduced to the universe very early, in fact production of them used to be orders of magnitudes higher at the beginning.
Supergiant and hypergiant stars (like Eta Carinae and SN 2006gy's progenitor) don't have long lifetimes and were likely prevalent in the early universe. Their deaths could have formed a lot of the heavy elements in HE 1523-0901. Five hundred million years is plenty of time for a lot of 100-120 solar mass giants to burn out and go supernova. It's likely the remnants of these early giants produced most of the stellar nurseries the next generation of less massive stars were born in.
I'm a loner Dottie, a Rebel.
That's correct. The star is metal-poor -- it's has an iron abundance (the standard measure of how much metals a star has) of [Fe/H] = -2.95. This is a lograthmic scale, and means that, on a scale where the sun is 0.0, HE1523 has about 1/1000th the amount of iron. The bracket notation means [Fe/H] = log10{N(Fe}/N(H)} - log10{N(Fe)/N(H)}_sun...i.e. the logarithmic difference of the number of atoms of Fe, compared to hydrogen, normalised to the solar ratio.
But the kicker is that HE1523 is very heavily r-process enhanced too...which means that it has a lot r-process, neutron-capture elements (think Uranium and thorium), compared to how much iron it has. HE1523 has [r/Fe] = 1.8....which means it has a 100 times more r-process heavy metals compared to iron, than does the sun.
BOTH of these factors are very important for this measurement, because you need to have very few metals, very high signal-to-noise data, very high resolution, and very strong r-process abundance, in order to be able to observe the uranium line. Anna needed 7.5hrs of VLT time to get a signal-to-noise ratio of about 350 or so...much higher than the S/N ~ 50-75 that we got from Magellan.
You can get a pdf of the paper here. Check out Fig 2, which shows the relevant part of the spectrum, with the Uranium line. See how it's right next to the booming Fe line...that's why we need a low iron abundance to do this work.